The invention relates to apparatus for treating running webs or strips of flexible material. More particularly, the invention relates to improvements in apparatus for treating (especially drying) web- or strip-shaped substrates which are coated at one side, e.g., with one or more layers of an adhesive substance containing a surplus of moisture (such as an evaporable solvent) which must be expelled prior to further treatment of the substrate.
It is known to train a coated web-like substrate over one or more rotary guide members in the form of rollers or drums while the substrate is being treated with a gaseous fluid, e.g., with a heated gas which is to expel moisture from the substrate and/or from its coat or coats. Apparatus of such character are known as drum type dryers and are often used to expel solvent from one or more layers which are applied to one side of a running substrate. Expulsion of moisture (such as an evaporable solvent) entails a solidification of the applied layer or layers. As a rule, the gaseous conditioning medium is caused to impinge directly upon the outer side of the single layer or upon the outer side of the outermost layer at one side of the running substrate. This entails rapid drying of the material at the exposed side of the single layer or at the exposed side of the outermost layer, and the thus obtained hardened film prevents evaporation of moisture from the inner stratum or strata of the layer or layers. Thus, the moisture which is caused to evaporate in the inner stratum or strata of the layer or layers at one side of the substrate is entrapped between the substrate and the hardened film at the outer side of the single layer or at the outer side of the outermost layer or layers.
The temperature of the gaseous conditioning medium can be lower than the temperature of the substrate, for example, if the temperature of the substrate has been raised during the preceding drying of the applied layer or layers. Such conditioning step then constitutes an additional operation which must be carried out prior to further processing of the substrate and contributes to the overall cost of the combined coating and conditioning operation.